Electromagnetic waves have been used in various applications to supply energy to objects. In the case of radio frequency (RF) radiation for example, RF energy may be supplied using a magnetron, which is typically tuned to a single frequency for supplying RF energy only in that frequency. One example of a commonly used device for supplying RF energy is a microwave oven. Typical microwave ovens supply RF energy at or about a single frequency of 2.45 GHz.
When RF energy is supplied to an antenna to be delivered to an object (e.g., an object placed in a cavity), usually only a portion of the supplied energy is dissipated in the object or delivered to the cavity. Part of the energy may be reflected back from the cavity to the antenna. If more than one antenna is located in the cavity, part of the energy emitted from one antenna may be coupled to the other antenna(s).